There are many safety devices which may be installed in motor vehicles for protection of the occupant(s) (i.e., the driver and/or passenger) during a collision. Passive safety systems, for example, perform their protective function without active manipulation by the occupant(s). Known passive safety systems typically include a driver's side air bag and optionally a passenger side air bag as a first passive safety system component. The air bag(s), being triggered by one or more acceleration sensors, is (are) inflated rapidly during a severe collision in order to cushion the frontal impact of the driver's and or passenger's upper torso and head against the steering wheel and/or dashboard. Known passive safety systems may also include a knee restraint protective device as a second component which is typically disposed beneath the dashboard. Like the airbag(s), the knee restraint is also rapidly inflated upon detection of a severe frontal impact for cushioning the knees and upper legs of the occupant(s).
While such passive system devices are effective in protecting most occupants from impacting the steering wheel and/or dashboard during a severe frontal collision to the vehicle, the effectiveness of the known passive safety system is reduced in the case of the "small" occupant. An example of a "small" occupant is a mature female having a physical stature which places her in the lowest five percent of the population (i.e., the so called "five percent woman"). During a severe frontal collision, a "small" occupant without a fastened seat belt will tend to slide from her seat and under the knee restraint device and thereby impact against the dashboard or steering column and suffer severe physical injury.
This sliding condition is made worse if the occupant's seat is set in the furthest rearward position (i.e., in a direction away from the dashboard) when the collision occurs. This situation typically occurs on the passenger side since it is often desirable to move the seat as far back as possible to provide a maximum amount of leg room. In such a situation, however, even normal sized and larger occupants are likely to slide off the seat and impact the dashboard before impacting the knee restraint or air bag protective device.
A possible solution to this problem could be achieved by simply restricting the rearward range of travel of the seat. However, this would unnecessarily restrict the comfort for all sizes of occupants.
Another solution would be to control the inflation process for the knee restraint device by taking into account the rearward position of the seat and the body size of the occupant. Such an approach is known, for example, from published European patent document EP-A0 357 225 wherein a passive safety system is disclosed for optimally controlling the inflation process of an air bag by taking into account: (1) the relative rearward position of a vehicle seat; (2) the body size of an occupant; and (3) the unfastened condition of the occupant's safety belt. A drawback with such an air bag inflation control system is that it requires expensive sensors to detect or monitor these conditions, as well as complicated actuators to perform the air bag inflation process. Also, a similar system for controlling the inflation process of a knee restraint device would likely be complex and costly.
For vehicles equipped with a passive safety system which includes both an air bag and knee restraint as previously described above, it is customary, and in some countries mandatory, to also provide safety belts as additional restraint systems. When the safety belts are worn, the above described risks are substantially reduced. However, it is well known that not all passengers will wear the safety belts all the time.
Accordingly, there is a definite need in the art for a simple and inexpensive motor vehicle safety device which releases a passenger occupied vehicle seat for forward movement in the event of a frontal collusion when the seat belt is not used for more effective engagement with an air bag and/or knee restraint device.